Apparatus for performing chemical reactions under pressure in a multi-stage reaction zone with external intermediary thermal conditioning

ABSTRACT

The invention concerns a process and an apparatus for performing chemical reactions under pressure in the presence of a solid catalyst in a multi-stage reaction zone, after external intermediary thermal conditioning. This process may be used for the synthesis of ammonia or methanol or for gasoline reforming. It is characterized in that at least one reaction fluid is introduced into at least one compartment, a first reaction effluent is recovered, a heat exchange takes place, outside the reaction zone, between a first effluent and an external heat exchange medium, then the first effluent is introduced into at least one subsequent compartment and a second reaction effluent is recovered from the subsequent compartment. The reaction fluid or reaction effluent circulates cross-wise in the compartments substantially perpendicularly to the reaction zone, the compartments being tight and of elongate shape, each compartment being adjacent to one or two other compartments, each group of two adjacent compartments comprising a common partition wall, either substantially parallel to generatrix or substantially oblique with respect thereto.

This is a division of application Ser. No. 07/146,665, filed Jan. 21,1988, now U.S. Pat. No. 5,045,568.

The invention concerns a process for performing chemical reactions underpressure from reaction fluids in the presence of at least one solidcatalyst, in a multi-stage reaction zone with external intermediarythermal conditioning. It also concerns a reactor for carrying out theprocess and the use of the reactor and of the process.

The invention may particularly be used for the synthesis of methanol, ofammonia, as well as for catalytic reforming, stabilizing hydrogenationof gasolines and hydrocracking of heavy oil cuts.

More generally, it is applicable to all processes using heterogeneouscatalysis wherein fluid reactants, either in liquid or gas state orcomprising both liquid and gas reactants, react with each other oversuccessive catalyst beds formed of particles, granules, spherical solidsor other solid elements or more or less complex and sophisticatedstructures.

BACKGROUND OF THE INVENTION

The concerned reactions generally develop reaction heat requiring one ormore intermediary thermal adjustments with an external medium.

It is known that chemical reactions developing much heat may beperformed in several steps with an intermediary thermal adjustment aftereach step.

Thus, the catalytic reforming of gasolines; for example; (see FrenchPatent 2,160,269; U.S. Pat. No. 4,210,519; and U.S. Pat. No. 4,233,268)is usually conducted in three reactors with solid catalyst bedsseparated by two external heating furnaces.

The use of so many reactors is expensive in equipment, pipes andinstallation costs.

For this reason it has often be proposed to arrange the differentreactors in a single reaction enclosure whose walls are adapted towithstand the relatively high internal pressure of the system.

For this purpose, the solid catalyst beds are vertically superposed andlay on supporting grids, or directly, on horizontal partition wallsFrench Patent 2,573,996.

These grids and partitions must withstand both the weight of thecatalyst bed and the strains resulting from the pressure drop generatedby the flow of reaction fluid through heat-transfer elements and throughthe catalyst bed itself.

These two strains result in extremely high totals, on the order of50-100 or even 150 tons per square meter, whereas the currentspecifications for industrial floors are limited to about 0.5-1 ton persquare meter.

In order to avoid this cumulative strain effect resulting inconstraining mechanical solutions as concerns as well the weight of thesupporting beams as the lost dead space, it has been proposed,particularly for methanol reactors (Hydrocarbon Processing, May 1984: p.95-100) to superpose reactors, not of the axial but of the radial type,where the catalyst is placed into a hollow cylindrical cartridge, oreven into several cartridges, and the reaction fluid flows horizontally,either centrifugally from the internal cylinder to the external cylinderor centripetally from the external cylinder to the internal cylinder.

This solution has the advantage of releasing the separation floors fromthe strains due to the reaction fluid circulation, but has thedisadvantage of leaving a large dead space, particularly a void centralcore which, according to British patent 1,140,071 can be used to house aheat exchanger.

A disadvantage of this solution, emphasized in U.S. Pat. No. 4,225,562in the difficulty of accurately centering the two cylinders defining thering of solid catalyst. A bad centering results in a heterogeneity ofthe fluid flow paths. Such a result is highly detrimental to goodperformance of the main reaction and results in excessive temperatureswhich are dangerous for the catalyst stability.

Another disadvantage is the requirement of charging and dischargingcatalyst cartridges. For this purpose, flanges of the same diameter asthat of the reactor can be provided, but this is not the best solutionwhen operating under pressure and with a reactor of large size. It isthen recommended to weld the generally hemispherical end parts to thecylindrical body. But for each catalyst discharge operation it isnecessary to saw off said end parts to withdraw the cartridges and tothen weld back said parts again after the reactor phase of reactorcharge. The operation is time-consuming, delicate and requires at eachtime administrative authorization and control.

On the other hand U.S. Pat. No. 4,225,562 teaches the provision ofcompartments after parallelpiped shaped as, arranged parallel to theenclosure axis. All of these compartments have the same sectional areaand volume.

The device uses to the best one half of the available space. In additionto the mechanical complexity and the corresponding high cost of thedevice, the standardization of compartments of identical volumeprecludes the adaptation of the catalyst volume to the variation of thereaction velocity.

Consequently, the device according to this patent can be used only withreactors either of the single stage type, as far as kinetics isconcerned, or performing reactions whose velocity is independent fromthe conversion rate, i.e., reactions of zero order.

Among the various embodiments of reactors with radial partitions, it isworth to mention the device disclosed in U.S. Pat. No. 3,898,049,wherein the catalyst cartridge is divided into tent 3 898 049, whereinseveral sectors in a longitudinal direction. The reaction fluidssuccessively pass through these sectors, alternately downwardly andupwardly, in the direction of the reaction enclosure longitudinal axis.It is easily observed that the proposed device is only applicable invery peculiar circumstances where the travel lengths, and hence thepressure drops, are unimportant since, with reference to an axialreactor of same height and, a fortiori, to a radial reactor, the fluidtravel is considerably extended in proportion to the number of sectionsof the cartridge.

The prior art is further illustrated by the British Patent 2 120 119disclosing a longitudinal reactor for conducting chemical syntheses ingas phase. This reactor comprises catalyst-containing parallelepipedenclosures arranged along the reactor axis and having permeable oppositewalls through which the charge circulates. The effluent may be innerlycooled by quench, thus limiting the available internal space.

French Patent 2,573,996 illustrates a catalytic reactor with only onecompartment for ammonia and methanol synthesis without internal heatexchanger. The wall temperature is maintained at a low level by thepresence of an air space.

German Patent 2,929,300 discloses an exchanger reactor with axial flowthrough catalyst zones of variable cross-section, these zones beingnon-adjacent.

OBJECTS OF THE INVENTION

A first object of the invention is hence to provide a multi-stageprocess and reactor, operating under pressure with external intermediarythermal conditioning. A main object of the invention is to provide aninexpensive reactor, easy to manufacture and to operate for charging anddischarging catalyst.

Another object is to provide a reactor where substantially the wholeavailable volume may be occupied by the catalyst.

Still another object is to provide for a better control of the fluidvelocity distribution through the catalyst beds so as to avoid localoverheatings having the fatal effect of deactivating the catalyst andhence of decreasing the period of use and disturbing the reactionextent.

Other objects of the invention and further advantages thereof will bemade apparent from the following description.

SUMMARY OF THE INVENTION

The invention concerns more particularly a process for conductingchemical reactions under pressure in a reaction zone comprising at leasttwo compartments, each of which contains, at least partly, at least onesolid catalyst wherein one reaction fluid is introduced into at leastone compartment and circulates therethrough. A first reaction effluentfrom said compartment is recovered and heat is exchanged, outside of thereaction zone, between the first effluent and an external heat exchangemedium. Said first effluent is then introduced after heat exchange withat least one subsequent compartment. Said first effluent flows throughsaid subsequent compartment and a second reaction effluent is recoveredfrom said subsequent compartment, said reaction zone being of elongateshape and comprising an enclosure with at least one generatrix, theprocess being characterized in that said reaction fluid, or reactioneffluent, flows cross-wise through said compartments in a directionsubstantially perpendicular to said generatrix, said compartments beingtight, of elongate shape in the direction of said generatrix, each ofsaid compartments being adjacent to one or to two other compartments,each group of two adjacent compartments comprising a common wall, eithersubstantially parallel to said generatrix or substantially oblique withrespect to the latter.

In these conditions, the reactor offers a good compromise betweenfilling and pressure drop level and further provides regular paths forthe fluid through the catalyst bed.

Instead of a substantially oblique common wall, the reactor may have awall comprising staggered sections in the same direction, each of thembeing parallel to the generatrix, but their assembly forming theequivalent of an oblique wall.

All these wall sections are so interconnected as to be fluid-tight. Thischaracteristic offers the advantage of varying the catalyst bedthickness in the reactor to improve the fluid distribution within thecatalyst mass over its whole height.

The reaction zone is advantageously cylindrical with circular base.

The length of each compartment and of each common wall is substantiallythat of the reaction zone and the cross-section of the compartment maybe substantially inscribed in the section of the enclosure.

When the reaction zone (section of the enclosure) is advantageouslycircular, the cross-section of the compartments may be inscribed in thecircle, defined by the section of the enclosure or in a circle coaxialtherewith.

All the compartments are hydrodynamically insulated and tight so that nocommunication is possible between the various compartments inside thereaction zone, through any wall. The fluid or reaction effluent usuallyenters a compartment through a port connected to an inner distributionzone of the compartment and flows out therefrom after cross-passage inthe whole catalyst bed, through an outlet connected to an innercollecting zone usually located at the opposite of the distributionzone.

The number of compartments and consequently of intermediary heatexchanges is variable. The section and/or volume of the compartments maybe identical or different and is advantageously determined in accordancewith the parameters and constraints of the process to be performed, forexample, the reaction velocity which depends on the conversion advancerate.

The invention also concerns an apparatus for carrying out the process.

Generally, it comprises:

a reactor adapted to contain at least one catalyst, having asubstantially cylindrical enclosure and comprising a first and a secondtight end,

at least two adjacent and tight compartments contained in said reactor,of elongate shape in the direction of said generatrix, each group of twoadjacent compartments comprising a common wall, either substantiallyparallel to said generatrix or substantially oblique with respectthereof, each compartment further comprising at least one intake meansfor the reaction fluid or reaction effluent into said compartment and atleast one outlet means for the reaction effluent having passed throughsaid compartment, said intake and outlet means communicating with thereactor through said enclosure.

at least one distribution means in each compartment adapted totransversally distribute into each compartment the reaction fluid orreaction effluent substantially perpendicularly to said generatrix andconnected to said intake means,

at least one means for collecting the reaction effluent from eachcompartment, connected to said compartment outlet means,

at least one heat transfer means interposed between said reactioneffluent outlet means of one of the compartments and said reactioneffluent intake means in the subsequent compartment.

Another transfer or heat exchange means consists, according to anotherembodiment, of using a mixture with a gas and advantageously with freshand relatively cold fluid or reaction effluent for cooling the effluentat the outlet from a compartment and before its admission to the nextcompartment, with the advantage of saving one or more exchangers. Forthis purpose, the reactor is generally provided with intake means forthis gas in order to produce said quench, said means being either insideor outside the reactor, preferably outside.

The reactor reaction zone, of elongate and preferably substantiallycylindrical shape, is generally divided, along its length,advantageously in a direction substantially parallel to the generatrix,into several compartments, by means of tight partitions which may bedirectly connected to the enclosure casing. The length of the tightpartition-walls along the generatrix is generally equal to the reactorlength.

The reaction fluid, consisting either of a gas or a liquid or agas-liquid mixture, passes successively through the so-definedcompartments, previously filled with solid catalyst.

The fluid, more precisely the reaction effluent, after partial reactionover the catalyst bed of one of the compartments is discharged from theenclosure, passes through a heat transfer apparatus where it is broughtto the adequate temperature and again penetrates the enclosure to passonto the next catalyst stage. The volume of each compartment isgenerally so adjusted that, in each compartment, the difference betweenthe compartment inlet and outlet temperatures is within the range fromabout 1 to 200° C. and preferably from 5 to 150° C.

This fluid passage generates pressure drops and pressure differencesbetween the adjacent compartments of the enclosure. These dynamicpressure differences produce, on the compartment walls, mechanicalstrains which may be very high and may require excessive metalthicknesses.

The common walls of the different compartments, may consist of verticalor oblique supported planar panels, or advantageously of self-bearingpanels of curved shape. They may be advantageously substantiallyparallel to the generatrix of the reaction zone.

When the panels are planar and supported, the supports preferablyconsist of stay-bars placed substantially perpendicularly to the planarpanels and connected both to the partition wall and to the reactionenclosure.

When the panels are of the self-bearing type, they preferably compriseeither assemblies of profiled sheets or cylindrical sectors, whosegeneratrices are substantially parallel to the reactor generatrix andwhose bases are shaped either as arcs of circle of radius ranging from0.1 to 100 times, preferably 0.5 to 50 times that of the reactionenclosure, or as portions of quadratic curves such parabolas,hyperbolas, or elipses.

Inside the compartments filled with solid catalyst elements, thereaction fluid or reaction effluent is introduced and distributed withinthe catalyst mass, through distributors forming the distribution zone.

The so-formed thin fluid jets, after passage through the catalyst bed,are collected and conveyed to the outlet by means of collectorsgenerally located at the opposite of the distributors, which form thecollecting zone.

The distributors and collectors are so arranged that the reaction fluid(and the effluent), instead of flowing in the longitudinal direction ofthe reaction zone, which considerably increases the travel of the fluidsand the pressure drops resulting therefrom, flows perpendicularly to theaxis of the cylinder forming the enclosure. The total travel of thefluid through the catalyst beds may generally be kept lower than twicethe length L, from tangent to tangent, of the casing or cylindrical wallof the reaction zone, preferably at most equal to said length L (seeFIG. 16, hereinafter defined).

For this purpose, the distributors and collectors may consist of pipeswhose sections are either circles, sectors of circles, polygons orplanes, or still sections commonly called "scallops". The area of thesections may vary along the generatrix in relation with the fluid flowrate at its level.

The pipes may be either parallel to the reactor generatrix or obliquewith respect thereto.

Inlet and outlet means for the reactor fluid or the reaction effluentmay be provided at any place in each compartment. However, they may beadvantageously placed so that the inlet means is substantially locatedat the level of one of the reactor (or compartment) ends and the outletmeans is located substantially at the level of the other end. Accordingto this embodiment, the section of the distributing pipes at the inletof the compartment is advantageously greater than that of the samedistribution pipe at the other end of the compartment, in view of thegreater gas flow rate at the inlet level and, conversely, the collectingpipe section is advantageously smaller at that inlet level, in view oflower flow rate of the gases collect at said level, than that of thesame collecting pipe at the outlet end of the compartment.

By this arrangement, a substantially constant gas velocity can bemaintained at any point of the distributor and of the collector, so thatfilling of the compartment with catalyst can be optimized.

For this purpose, according to a particular embodiment, the wall of thedistributor and of the collector may comprise, on the parts facing thecatalyst bed, at least one distribution or collecting section (a grid,for example) substantially parallel to the generatrix, or at least onedistribution and collecting section substantially oblique with respectto said generatrix, each of said distribution and collecting sectionsbeing staggered in the same direction with respect to each other, sothat the fluids pass through a constant thickness of Catalyst bed.

The number of distributors may be higher or lower than the number ofcollectors. Preferably, the number of distributors is the same as thenumber of collectors, so as to provide for a good distribution of thegas flow.

When only a few number, at most three, of distributors and collectors isused in a compartment, they may be placed against the enclosure, nearthe junction member between the enclosure wall and the commonpartition-walls. This solution is particularly advantageous whentreating low flow rates and is very easy to perform. The flow of fluidand reaction effluent is then substantially parallel to the commonpartition-walls.

Preferably, when there are at least four distributors or collectors theyare distributed along the common partition-walls and optionally on theenclosure wall parts facing said partition-walls. This arrangementprovides for the treatment of high flow rates of fluid and of reactioneffluent. It requires a circulation of fluid and of the reactioneffluent substantially perpendicularly to the tight commonpartition-walls of the compartments.

For distributing or collecting the reaction fluid, the distributors andcollectors may be either pierced with holes or consist of grids withopenings formed between metal wires, either crossed or parallel, andwhose profiles may be so determined as to obtain a maximum fluid flow.

In certain compartments, the average travel of a thin fluid jet from adistributor to a collector, or distance from the distributor to thecollector may be identical for the different distributors, but thisaverage travel of a fluid jet may vary from one distributor to another.

Preferably, the opening cross-sectional area on the catalyst bed of thedistributor and of the collector facing it is variable in relation withthe length of the average travel between these elements, i.e. thedistance between the distributor and the collector facing it.

These different characteristics as well as other elements formingintegral parts of the invention are described more in detailhereinafter.

According to one embodiment, the reaction fluid and the effluents mayflow substantially parallel to the common partition wall defining twoadjacent compartments, this being advantageous when the catalyst volumesare substantially of the same order in the different compartments.

According to another embodiment of the process, the reaction fluid andeffluents circulate substantially perpendicularly to said wall,particularly when the distributors or collectors are located on saidwall.

This embodiment is particularly advantageous when the catalyst volumesare very different in the different compartments.

The fluid velocity in the compartments, generally ranges from 1 to 200m/s and preferably from 5 m/s to 100 m/s and, of course, depends on theselected reaction and operating conditions.

The temperatures of the fluids in the various compartments is generallyfrom 100 to 800° C., preferably from 200 to 600° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its advantages made clearlyapparent from exemplified embodiments described in relation with theaccompanying drawings, whose figures diagrammatically illustrate, in anon-limitative manner, the apparatus and the process, and wherein:

FIGS. 1A, 1B, 1C and 1D represent different embodiments of the processand of the reactor according to the invention;

FIGS. 2, 3, 4, 5 and 6 show different types of tight commonpartition-walls;

FIGS. 7, 8, 9, 10, 11, 12 and 13 illustrate different types ofdistributors and collectors and different fluid and reaction effluentcirculation modes;

FIGS. 14 and 15 show a partial cross-section of the reactor,substantially at the level of each end part thereof, along lines AA andBB; and

FIG. 16 is a longitudinal cross-sectional view of the reactor.

In FIGS. 1A, 1B, 1C and 1D the same elements of the device according tothe invention have been designated with the same reference number,respectively followed with letters a, b, c and d.

For example, when using the apparatus according to the invention formethanol synthesis (FIG. 1A), a mixture mainly containing hydrogen andcarbon oxides is supplied through the inlet pipe 1a to the top ofreactor 2a containing a catalyst of the type of those disclosed in thebook "Applied Industrial Catalysis" (Vol. 2, Chap. 6, p. 226 et sef.).

Reactor 2a, which is a vertical cylinder comprising a casing 10 ofcylindrical section and circular base, closed at both ends by ellipsoidend parts or preferably by hemispherical end parts (30 and 31, FIG. 16)is divided into three compartments without internal communication, 201a,202a and 203a, respectively of increasing volumes V1<V2<V3, by means oftwo internal tight plane walls (210a and 211a) which may be secured, forexample, by welding to casing 10 and to end parts 30 and 31, arrangedsubstantially parallel to the generatrix of reactor 2a.

The catalyst has been charged from the upper end part of the reactorinto the various compartments. All of the cross-sections of thecompartments are inscribed into the casing 10 of circular base.

The reaction fluid, having a pressure and a temperature previouslyadjusted respectively to 8 MPa and to about 250° C., is introduced intocompartment 201a substantially parallel to the common partition-wall,through at least one distributor 20 pierced with holes 12 (FIG. 8)generally scattered about its external wall facing the collector. Incontact with catalyst 11 in the compartment, hydrogen combines with thecarbon oxides to give methanol according to equations:

    CO+2H.sub.2 →CH.sub.3 OH                            (1)

    CO.sub.2 +3H.sub.2 →CH.sub.3 OH+H.sub.2 O           (2)

Reactions (1) and (2) are exothermic and, as the reaction progresses,the temperature of the fluid or of the reaction effluent increases.

When the temperature increase of the reaction effluent reaches 20 to 60°C., which corresponds to about 1-3% by volume of methanol present in thegas, the latter is withdrawn from compartment 201a through at least onecollector 21 pierced with holes 12 (FIG. 8) or of the grid type andconveyed through line 3a of the lower part towards a known, per se heattransfer means, 4a e.g. an external cooler, which brings it backsubstantially to its initial temperature at which it was fed to 201a.Instead of a heat exchange at 4a, a quench may be performed by means 4ffor introducing at least a part of the reaction fluid or of the coldeffluent into the line conveying the effluent to the next compartment.

From cooler 4a, which may be either an air-cooler or a heat-recoveryapparatus preheating for example all or a part of the charge orproducing hot water or steam under pressure, the gas mixture is fed,through line 5a, to the top of reactor 2a where it is introduced,through at least one distributor 22, into compartment 202a,symmetrically opposite to compartment 201a.

When, as a result of the reaction, the gas temperature is againincreased by 20-60° C. above its intake temperature, the reactioneffluent is again withdrawn through at least one collector 23 in thelower part of the reactor, conveyed through line 6a to cooler 7a whichagain brings it back to the initial optimum temperature. From 7a, thefluid flows through line 8a to the upper part of the reactor to reachcompartment 203a of reactor 2a through at least one distributor 24.

At the outlet from 203a, the mixture, which finally contains from 2 to12% by volume of methanol, is fed, through collector 25 and line 9a,into the lower part of the reactor, to the unit for condensation andpurification of the synthesized alcohol.

According to said FIG. 1A , the fluid and the reaction effluent flowcross-wise, substantially perpendicular to the reactor generatrix andparallel to the common partition-walls.

Compartments 201a, 202a and 203a may be placed side-by-side, compartment202a being in central position. Said order minimizes the strainsresulting from the pressure differences applied onto the commonpartition-walls 210a and 211a.

In a preferred arrangement, the last compartment 203a (FIG. 1A) is incentral position between the two first compartments 201a and 202a.

As a matter of fact, comparative surveys have shown that thisarrangement is the most favorable for optimizing the available effectivespace.

In the above description (FIG. 1A) the reactor 2a is placed vertically.

Depending on the local requirements, for example, when the ground isspongy and soft, reactor 2 may be arranged horizontally according toanother embodiment, as illustrated in FIG. 1B.

In this alternative embodiment, lines 1b, 3b, 5b, 6b, 8b and 9b arepreferably so arranged that the reaction fluid flows downwardlysubstantially parallel to the common partition-wall, thus avoiding therisk of destabilization of the catalyst bed by blowing of the catalystparticles.

FIG. 1C, illustrating another embodiment, shows a reaction system forgasoline catalytic reforming, which is endothermic. The diagramsimultaneously illustrates an where the fluid and the reaction effluentflow perpendicular to walls 210c and 211c, in compartments 201c and202c, and where they flow parallel to said same walls in compartment203c.

Through line 1c, naphtha vapors and recycled hydrogen circulate. The gasand naphtha vapor mixture is previously conditioned at about 0.5-3 MPaand about 500-530° C. In compartment 201c of reactor 2c, the reformingcatalyst, which may consist of platinum deposited on acid carrier anddoped with other noble metals such as for example, rhenium, is used tosubject naphtha essentially to dehydrogenation reactions which stronglydecrease the temperature of the reaction fluid to about 450-480° C. Thisfluid is then removed from compartment 201c and conveyed through line 3cto the external furnace 4c, of known type, where it is heated to about500° C.

The fluid is then supplied through line 5c to compartment 202c. Incompartment 202c, in addition to dehydrogenation, molecule rearrangementreactions are performed and the temperature decrease is much lesssubstantial.

When said temperature decrease reaches about 10 to 30° C., the fluidflows out from the second compartment 202c and is again heated to about500° C. in furnace 7c.

The third compartment 203c is substantially isothermal. As a matter offact, in addition to the dehydrogenation and molecular rearrangementreactions hydrogenation reactions occur which are exothermic and thereaction heat thereof compensates for the heat loss due to reformingproper.

The processes of the invention according to FIGS. 1A, 1B and 1C areapplicable to reactors in which different compartments are seriallyconnected, so as to form a succession of, stages, in the kinetic meaningof the word.

They also apply to multi-stage reactors, some compartments of which maybe connected in parallel (FIG. 1D) to form together either the first orthe last reaction stage.

This particular embodiment may be advantageous for certain reactions,particularly for ammonia synthesis.

As a matter of fact, it is known, at present, to operate this synthesisunder relatively mild conditions (pressure of about 10 MPa andtemperature of about 400° C.) an , in these conditions, it is no longernecessary to provide a double jacket for cooling the external wall ofthe reaction enclosure.

However, for these reactors without wall cooling, called "hot-wallreactors", difficulties arise due to the pressure drops resulting fromthe large volume of gas flowing through the catalyst bed.

By dividing the gas flow rate by two at critical locations, thisdifficulty can be evaded.

FIG. 1D diagrammatically shows a reactor for ammonia synthesis, built inconformity with the process of the invention.

A mixture of synthesis gases containing about 25% nitrogen, 75% hydrogenand ammonia and argon traces (<5%) are introduced under about 10 MPa andat 350-400° C. through line 1d. Line 1d is extended by two lines 1d1 and1d2 conveying said gas into the two compartments 201d1 and 201d2,advantageously of equal volumes and of equal sections, symmetricallyarranged with respect to the axis of the cylinder defining the reactionvolume.

Due to this parallel connection, the volume of said first catalyststage, although small with respect to the volume flow of the synthesisgas, finally offers only little resistance to the gas flow.

At the outlet of compartments in parallel 201d1 and 202d2, the synthesisgas contains about 4-7% of ammonia and its temperature is increased byabout 40-60° C.

Gases flowing through lines 3d1 and 3d2 are supplied through line 3d toexchanger 4d, for heat recovery.

At the output of exchanger 4d, the gases, cooled at the optimumtemperature of about 350-400° C., are conveyed through line 5d to thecentral compartment 202d of reactor 2d.

The effluent gases from reactor 2d, which contain about 8 to 14% byvolume of ammonia approximately at a temperature of 400-450° C. andunder a pressure of about 10 MPa, are fed through line 6d to the ammoniaconditioning and recovery unit placed after the reaction section.

In the described reactors (FIGS. 1A, 1B, 1C) the partition-walls 210 and211, although released from the weight of the catalyst, directly layingonto the enclosure wall, have to nevertheless resist generally thethrust resulting from the pressure difference between adjacentcompartments 201-203 on the one hand, 203-202 on the other hand.

These pressure differences are due to the pressure drop through thecatalyst beds and the heat transfer apparatuses and are on the order of0.1-0.4 MPa. They may even reach 1 MPa when using heating furnaces as,for example, in reforming operations.

In the example of methanol, synthesis reactor, shown in FIG. 1A, thewall 210a (for example) of 3200 mm width and 20 mm thickness, isdesigned to resist to a pressure difference of 0.3 MPa.

When using a bearing system parallel to the plane of said wall, beams ofHEM 400 type, distributed every 500 mm (FIG. 2) are convenient.

With a perpendicular bearing system, stay-bars of 25 mm diameter,arranged in square mesh pattern of 500 mm side, can be used, forexample. These stay-bars are connected to the partition-walls 211 and tothe wall of the reaction enclosure 10 (FIG. 3).

The planar wall with its relatively bulky bearing systems difficult tofix, may be replaced by a simple wall of special shape, so designed asto alone withstand the pressure.

When using a self-bearing form, the profiles may have the samethickness, for example, as that of the planar wall 210a (20 mm) of thetype shown in FIG. 4 with a height of, for example, 300 mm and a pitchof 395 mm.

FIGS. 5 and 6 show other self-bearing forms according to the inventionwith convex and concave sides oriented towards compartments 201 and 202.A combination of these various forms may also be used. These forms arepreferred to those shown in FIG. 4 since they facilitate the connectionbetween these walls and the wall of the cylindrical reactor.

The walls 210 and 211 are cylinder sectors whose generatrices aresubstantially parallel to the generatrix of the reaction enclosure andwhose bases are arcs of circle of radius ranging from 0.1 to 100 times,preferably 0.5 to 50 times that of the reaction enclosure.

In the reactors according to the invention, the reaction fluids flowcross-wise, perpendicular to the enclosure generatrix. Accordingly,distributors 20, 22, 24 and collectors 21, 23, 25 are preferably formedof pipes substantially parallel to said generatrix, whose openings 12are generally scattered about their walls in the direction of thecatalyst bed.

Preferably, the cross-section of the distribution (20, 22, 24) and/orcollecting (21, 23, 25) pipes may be shaped as shown in the figures,either as a circle (FIG. 7) or as a sector formed at the junctionbetween the reactor wall and the common partition wall and closed by aplane (FIG. 8) or by a cylinder portion of circular base (FIG. 9), thefluids then flowing substantially parallel to the commonpartition-walls.

When the total cross-section of the distributors or of the collectorsamounts to more than 10%, preferably more than 20% of that reserved forthe catalyst, distributors 20, 22, 24 and collectors 21, 23, 25preferably consist of several pipes (FIGS. 10, 11 and 12) substantiallyparallel and distributed along the common partition-wall 210 andoptionally along the part of the reaction enclosure wall 211 facing it;the flow direction is then substantially perpendicular to the commonpartition-walls.

These different distribution pipes 20a, 20b, 20c . . . of the firstcompartment, 22a, 22b, 22c . . . , of the second compartment and 24a,24b, 24c . . . , of the third compartment, as well as the differentcollecting pipes 21a, 21b, 21c . . . , 23a, 23b, 23c . . . , 25a, 25b,25c, respectively of the first, second and third compartments, may beshaped as sectors of circle (FIG. 10) or of polygones, for exampletriangles (FIG. 12), or squares or rectangles (FIG. 11). In theembodiment illustrated in FIG. 11, the number of distributors 24 islower than the number of collectors 25, but conversely, a reactor couldhave been built as well with a number of collectors lower than thenumber of distributors.

FIG. 13 shows another embodiment of distributors and collectors shapedeither as an arc of circle 20, 22 close to the casing, or plane 21, 23,24, 25 close to the common partition-walls 210 and 211.

According to these various embodiments, a larger cross-section ofopenings 12 compensates for the lower number of distributors orcollectors.

The openings 12 for introducing and collecting fluids may be of anyshape, for example circular, and their cross-sectional area isadvantageously proportional to the average travel corresponding to eachdistributor-collector pair so as to minimize the preferential passagesof the gases.

As shown in FIGS. 14, 15 and 16, illustrating an embodiment of thedistribution and collecting means, the line 1a of FIG. 1A issubstantially placed at the level of one of the end parts 30 of thereactor or of the first compartment 201a, whereas the output line 3a isplaced substantially at the level of the other end part 31 of thereactor or of the first compartment. The cross-section of thedistribution duct, for example 20, in compartment 201a, at the level ofend part 30 (FIG. 14, AA-cut) is greater than at the level of end part31 (FIG. 15, BB-cut) whereas the cross-section of collecting duct 21 atthe level of end part 30 is smaller than that of collecting duct 21 atthe level of end part 31. The same is true for the sections of the otherdistribution ducts 22, 24 and collecting ducts 23, 25 in the othercompartments (FIG. 14, 15).

According to FIG. 16, illustrating more particularly this embodiment,the walls of distributor 20 and collector 21 facing the catalyst bed,may comprise sections (grids with holes 12, for example) substantiallyparallel to the generatrix and staggered with respect to one another inthe same direction, so that the thickness of the bed traversed by thefluids is the same all along the reactor and said walls are oblique as awhole with respect to the generatrix.

The operations of charging the catalyst may generally be performedthrough at least one opening 32 in the upper end part of the reactor andpreferably through at least one opening per compartment. For horizontalreactors with vertical common partition-walls 210b and 211b (FIG. 1B),the catalyst may be charged through openings generally provided in thereactor casing at the level of each compartment.

The catalyst is generally discharged from the bottom through at leastone exhaust port 33 and preferably through one port in each compartment.These charging and discharging operations are easily performed and thusthe reactor did not stand idle for a long time.

The reactor walls (those of the casing and of the common partitions) maybe heat insulated. An intermediary fluid, introduced for heating orcooling, may optionally circulate within the partition-walls,particularly the common partition-walls of adjacent compartments.

The above-figures only show a reactor with three compartments and twoheat-transfer means, for sake of clarity. Obviously, it is possible tobuild a reactor according to the invention having a plurality ofcompartments, for example 3 to 10 and of intermediary heat-transfermeans.

What is claimed is:
 1. An apparatus for conducting chemical reactions,comprising:a reactor of elongated shape containing at least one catalystbed, said reactor comprising a substantially cylindrical casing having ageneratrix, and first and second tight end parts; at least two tightadjacent compartments contained in said reactor of elongated shape, saidcompartments extending lengthwise, in the direction of the generatrix,along substantially the entire length of said reactor; each group of twoadjacent compartments having a common partition-wall, said commonpartition-wall having a longitudinal axis which is either substantiallyparallel to said generatrix or substantially oblique with respectthereto, said common partition-wall being in fluid tight connection withsaid casing, and each of said compartments having a first end and asecond end opposite said first end; each compartment further comprisingat least one inlet means located at said first end for introduction offluid into said compartment and at least one outlet means located atsaid second end for removal of fluid which has passed through saidcompartment, said inlet and outlet means being in fluid communicationwith the exterior of said reactor through said casing; at least onedistribution means in each of said compartments for crosswisedistributing fluid in a direction substantially perpendicular to saidgeneratrix, said at least one distribution means being in fluidcommunication with said at least one inlet means; at least onecollecting means in each of said compartments for removing fluidtherefrom, said at least one collecting means being in fluidcommunication with said at least one outlet means, whereby fluidintroduced into each of said compartments via said at least one inletmeans is distributed by said at least one distribution means, traversessaid compartment from said first end to said second end, is collected bysaid at least one collecting means, and is removed by said at least oneoutlet means; and at least one heat transfer means interposed betweensaid at least one outlet means of one of said compartments and said atleast one inlet means of another of said compartments, said at least oneheat transfer means being external to said casing.
 2. An apparatusaccording to clam 1, wherein said cylindrical casing has a base ofcircular section.
 3. An apparatus according to claim 1, wherein saidcommon partition-wall comprises planar panels.
 4. An apparatus accordingto claim 1, wherein said common partition-wall comprises self-bearingpanels of curved shape.
 5. An apparatus according to claim 4, whereinthe base of the self-panels of curved shape is shaped as an arc ofcircle of radius ranging from 0.1 to 100 times that of the reactor, oris shaped as a portion of a quadratic curve.
 6. An apparatus accordingto claim 1, wherein said distribution means and said collecting meansare arranged substantially parallel to said generatrix in eachcompartment.
 7. An apparatus according to claim 1, wherein said inletand outlet means are respectively located proximate to said reactorfirst end part and said reactor second end part, each of said at leastone distribution means and at least one collecting means extendinglengthwise in the direction of said generatrix, the cross-sectional areaof said at least one distribution means, proximate said reactor firstend part, being larger than the cross-sectional area of said at leastone distribution means proximate said reactor second end part, and thecross-sectional area of said at least one collecting means proximatesaid reactor first end part being smaller than that of said at least onecollecting means proximate said reactor second end part.
 8. An apparatusaccording to claim 7, wherein said at least one distribution and atleast one collecting means of each of said compartments comprising,respectively, more than one distribution or more than one collectingsections, each of said sections being substantially parallel to saidgeneratrix or substantially oblique with respect to said generatrix,each of said sections having an axis, the axis of each of saiddistributing sections being out of line with respect to one another, andthe axis of each of said collecting sections being out of line withrespect to one another.
 9. An apparatus according to claim 1, whereineach of said distribution means having means defining a plurality offluid outlets arranged along the length of said distribution means, andeach of said collecting means having means defining a plurality of fluidinlets arranged along the length of said collecting means.
 10. Anapparatus according to claim 1, wherein said reactor is horizontal andcomprises at least one substantially vertical common partition-wall. 11.An apparatus according to claim 1 comprising cold gas feeding meansinterposed between said outlet means of one of said compartments andsaid inlet means of another of said compartments.
 12. An apparatus forconducting chemical reactions, comprising:a reactor of elongated shapecontaining at least one catalyst bed, said reactor comprising asubstantially cylindrical casing having a longitudinal axis and firstand second tight end parts; at least two adjacent compartments containedin said reactor of elongated shape, said compartments extendinglengthwise, in the direction of said longitudinal axis, alongsubstantially the entire length of said reactor, each group of twoadjacent compartments comprising a common partition-wall, said commonpartition-wall having a longitudinal axis which is either substantiallyparallel to said longitudinal axis of said casing of substantiallyoblique with respect thereto, said common partition-wall being in fluidtight connection with said casing, and each of said compartments havinga first end and a second end opposite said first end; each compartmentfurther comprising at least one inlet means located at said first endfor introduction of fluid into said compartment and at least one outletmeans located at said second end for removal of fluid which has passedthrough said compartment, said inlet and outlet means being in fluidcommunication with the exterior of said reactor through said casing; atleast one distribution means in each of said compartments for cross-wisedistributing fluid in a direction substantially perpendicular to saidlongitudinal axis, said distribution means being in fluid communicationwith said at least one inlet means; at least one collecting means ineach of said compartments for removing fluid therefrom, said at leastone collecting means being in fluid communication with said at least oneoutlet means, whereby fluid introduced into each of said compartmentsvia said at least one inlet means is distributed by said at least onedistribution means, traverses said compartment from said first end tosaid second end, is collected by said at least one collecting means, andis removed by said at least one outlet means; and at least one heattransfer means interposed between said at least one outlet means of oneof said compartments and said at least one inlet means of another ofsaid compartments.